There are a number of factors to be considered in the formulation of a foam control material for use in controlling foam in pulp mill and paper mill operations and other operations, to eliminate or minimize the interference of foam in the particular operation. A foam control material should have the ability to decrease an already-formed foam to a low level in a short period of time and, additionally, the ability to prevent the formation of foam from the liquor once the material is present, over an extended period of time.
Foaming occurs in pulp and paper mills at a number of locations and many formulations have been suggested to control such foam, with the individual formulations being constructed for the particular location. Such locations include the brown stock washer wherein hot pulp is washed to remove entrained pulping liquor, the screen room wherein the washed pulp from the brown stock washer is subjected to displacement washing and cooling prior to passage to the bleach plant, and the paper making machine wherein the bleached pulp is formed into paper. In the first two locations, foaming occurs in alkaline medium, while, in the latter case, foaming occurs in an acid medium.
To date an effective defoamer composition which can control foam at all these locations and hence is effective over a wide temperature and pH range, has not been commercially available. The present invention provides a defoamer composition which is effective in foam control at each of these pulp and paper mill locations and, additionally is effective in foam control in other applications, including foaming in industrial effluents.
Many of the currently-available defoamer compositions consist predominantly of a mineral oil carrier for the active defoamer. To achieve dispersion of the oil-based material in the aqueous pulp and paper mill liquors to achieve the foam control, various spreading agents have been used. The compositions containing such spreading agents are introduced directly to the aqueous liquor in which the foaming is controlled. This may lead to inefficient utilization of the defoaming composition as a result of uneven dispersion of the compositions in the liquor. Attempts to form oil-in-water emulsions from such defoaming compositions has not met with success.